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Here is a little story about a king and his profits:
I bought 250 pieces of armor with buy orders for 20 copper. I listed all of them for 1 silver 20 copper. 40 sold, but then the undercutters started coming into the picture. So I used my sword and hacked the items off the market, then undercut all those jerks trying to enter into my kingdom! At 99 copper, another 75 of my items sold.
More undercutters came, and I once again had to cancel and relist. At 86 copper, I made all but 62 of my auctions sell. Finally, I beat the last of the undercutters at the 40 copper range.
Cancelling cost me a significant amount of my profit, as it would have been nice to sell all of them for 6 times the initial cost (before fees), but I still managed to sell 250 pieces of armor super fast (3 days).
This was one market, imagine how great this strategy works when you have 20-40 of the same kind of thing going on. Posting can take time initially, especially because all the different items come in jumbled up. Also sucks when you get that error.
Just be careful and don't screw up your margins! Cancelling too much on too many items will reduce your profit down into the negatives. Also, all your markets to recover back up to around where you started!